JP2004212543A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device where toner is hardly accumulated on fixing rotary bodies such as a fixing roller and a pressure roller. <P>SOLUTION: When the fixing roller 52 and the pressure roller 54 stand by, the temperature of a halogen heater 56 is controlled so as to set the temperature of a fixing nip part 58 at temperature Ts equal to or lower than temperature at which toner has maximum viscosity so that the toner stuck to the fixing roller 52 and the pressure roller 54 is prevented from being turned into a high molecular state and fixed to the fixing nip part 58. In the case of starting printing, the fixing roller 52 and the pressure roller 54 are idly rotated by preceding to the start of the printing. At the time of idle rotation, the temperature of the halogen heater 56 is controlled so that the temperature of the fixing nip part 58 becomes temperature T1 at which the toner has maximum viscosity. In the state of keeping the temperature of the fixing nip part 58 at the temperature T1, the fixing roller 52 and the pressure roller 54 are rotated for only time within the range of 10 to 15 seconds so as to soften the toner stuck to them. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００５５】
表１に示すように、１４０℃が最も糸状に引く状態となったので、本実施形態のトナーが最も粘度をもつ温度Ｔ１を１４０℃とした。
【００５６】
従来の温度制御（待機中では定着ニップ部５８の温度を定着温度（ここでは１７５℃）にする制御をいう）を実施して、印字率４％の原稿で間欠耐久（ここでは、１０分間に２枚の記録媒体に画像形成する）を行った。この場合、約１５００枚の記録媒体に画像を形成した時点で加圧ローラ５４にトナー汚れが発生した。
【００５７】
これに対し、本実施形態の技術（待機中では定着ニップ部５８の温度を温度Ｔｓ（ここでは１４０℃）に制御し、その後、空回転（前回転）のときには定着ニップ部５８の温度を温度Ｔ１（ここでは１４０℃）に制御する技術をいう）では、加圧ローラ５４に付着するトナー量を半分以下に軽減させることが可能となり、間欠耐久３，０００枚でも定着ローラ５２と加圧ローラ５４にトナー汚れが発生しなかった。また、本実施形態の技術では、定着ローラ５２と加圧ローラ５４の表面コートの粗さ等にバラツキがあった場合でも、各ローラのトナー付着を有効に防止できるので、表面コートを必要以上に高精度にする必要がなくなる。このため、歩留まり向上によりコストダウンを図ることが可能となる。
【００５８】
上記したハロゲンヒータ５６の温度を制御して定着ニップ部５８の温度を変動させる第２実施形態について説明する。
【００５９】
上記した第１実施形態のように温度制御しながら画像形成する場合、記録媒体が定着ニップ部５８を通過中に、レーザビームプリンタ１０の異常検知により定着ローラ５２と加圧ローラ５４が停止することがある。この場合、記録媒体が定着ニップ部５８に挟持されたままとなるので、定着ニップ部５８では大量のトナーが定着ローラ５２と加圧ローラ５４に付着する。定着ローラ５２と加圧ローラ５４が回転を再開した後に定着ニップ部５８を通過する１枚目の記録媒体には、ある程度のトナーが転移する。しかし、大半のトナーは定着ローラ５２若しくは加圧ローラ５４に付着したままの状態である。このため、連続プリントをする場合、定着ローラ５２若しくは加圧ローラ５４の表面に残ったトナーは離型性が低下するので、画像上にオフセットした状態が長く続くことがある。
【００６０】
第２実施形態の技術によれば、定着ニップ部５８を記録媒体が通過中に、レーザビームプリンタ１０の異常検知により定着ローラ５２と加圧ローラ５４が停止した場合であっても、定着ローラ５２と加圧ローラ５４の表面にトナーをほとんど蓄積させない。
【００６１】
第２実施形態について説明する。
【００６２】
第２実施形態では、第１実施形態と同じ構成の定着装置５０を使用する。
【００６３】
記録媒体１１が定着ニップ部５８を通過中に、レーザビームプリンタ１０が異常検知したときは定着ローラ５２と加圧ローラ５４が停止する。その後に、定着を再開するときは、定着ローラ５２と加圧ローラ５４を空回転させる。この空回転の際は、定着ニップ部５８の温度が、トナーが最も粘度をもつ温度Ｔ１（１４０℃）になるようにハロゲンヒータ５６を制御する。この状態で、定着ローラ５２と加圧ローラ５４を１０〜１５秒間だけ空回転させる。この空回転の直後に約６秒で定着ニップ部５８が定着温度Ｔ２になるようにハロゲンヒータ５６を制御し、定着ニップ部５８に白紙（クリーニング用の記録媒体の一例である）を１枚通過させる。
【００６４】
上記した１枚の白紙には、定着ローラ５２と加圧ローラ５４に付着している大量のトナーが転移する。この結果、実際の印字時にはオフセットトナーのない画像を得ることができる。また、定着ローラ５２と加圧ローラ５４に付着したトナーを除去することによってこれらのローラ５２，５４の耐久性も向上する。
【００６５】
ここで、印紙率４％の原稿を用いて、間欠耐久２枚／１０分（１０分間に２枚の記録媒体に画像形成する）を１セットとして、１５セット毎に定着ニップ部５８に記録媒体を１０秒間停止させてから再起動させる試験を行った。
【００６６】
上記した従来の温度制御（レーザビームプリンタ１０の電源がオンにはなっているが、定着装置５０で記録媒体にトナーを定着していないとき（待機中）は、定着ニップ部５８の温度が定着温度（ここでは１７５℃）になるように制御している、以下、この制御を従来の温度制御という）で試験を行うと、約５００枚で加圧ローラ５４にトナー汚れが発生した。これに対し、第２実施形態の技術では、加圧ローラ５４に付着するトナーの量を半分以下に軽減させることが可能となり、間欠耐久４０００枚でもトナー汚れが発生しなかった。
【００６７】
第３実施形態について説明する。
上述した第１実施形態と第２発明の実施の形態では、定着ローラ５２や加圧ローラ５４に付着しているトナーに、空回転（前回転）のときに粘着性をもたせて記録媒体に転移させることにより、これらのローラ５２，５４に付着するトナーや紙粉等の汚れを抑えた。この結果、定着装置５０の耐久寿命を引き延ばすこともできる。また、これによって定着ローラ５２と加圧ローラ５４の汚れはかなり軽減された。
【００６８】
しかし、プリント毎及び停止後の立上動作復帰毎に前回転を１０秒間行うと、感光ドラム１２や転写ローラ２２が摩耗して耐久性が低下する。また、プリント開始から排紙完了までの時間も長くなるため、省電力も不利になって使い勝手も悪くなる。
【００６９】
そこで、これらを解消する技術を、図５を参照して説明する。
【００７０】
図５は、第３実施形態の定着装置を示す模式図である。この図では、図２に示された構成要素と同一の構成要素には同一の符号が付されている。
【００７１】
第３実施形態の定着装置１００では、第１実施形態の定着装置５０に印字率演算装置１０２（ＣＰＵ）を加えた。この印字率演算装置１０２では、原稿の全表面積に対する画像の割合（印字率）が演算される。印字率演算装置１０２で演算された原稿一枚あたりの印字率から、定着ローラ５２や加圧ローラ５４に付着するトナーを予測する。この予測付着トナー量が所定量を超えた時点で、トナーが最も粘度をもつ温度Ｔ１（１４０℃）に定着ニップ部５８がなるように制御装置６２でハロゲンヒータ５６を制御して、定着ローラ５２と加圧ローラ５４を１０秒間だけ空回転させる。この空回転の後、定着ニップ部５８が定着温度Ｔ２（１７５℃）になるように制御装置６２でハロゲンヒータ５６を制御し始めて、その６秒後に定着ニップ部５８に記録媒体を搬送させる。
【００７２】
図６を参照して、定着ローラや加圧ローラに付着するトナーの量の予測について説明する。図６は、予測付着トナーを示すグラフである。この図における予測付着トナー量は、印字率及びトナー濃度と加圧ローラに付着する量を予測するために、紙種は厚めの紙坪量８０ｇ／ｍ^２で表面性が悪いカンガス紙を用いた。このような記録媒体を使用して、定着ローラ５２と加圧ローラ５４が完全に冷えた状態から連続して１０００枚の記録媒体に画像を形成し、５００枚毎に、各ローラ５２，５４の汚れを透明テープ（マイラーテープ）で採取して反射濃度（東京電色製ＲＥＦＬＥＣＴＯＭＥＴＥＲ ＭＯＤＥＬ ＴＣ−６ＤＳ）を測定した。この反射濃度から付着トナー量を予測した。
【００７３】
このようにして反射濃度を測定した結果、印字率４％の原稿の場合は、原稿１枚あたり反射濃度約０．００８８に相当するトナーがローラに付着し続けて増加することが判明した。また、印字率４０％の原稿の場合は、原稿１枚当たり反射濃度約０．０１２９に相当するトナーがローラに付着し続けて増加することが判明した。従って、印字率が１０倍に増えるとトナー付着量は約１．５倍増えることになる。この実験から１枚あたりの印字率とトナー付着量の設定を図７のように設定した。
【００７４】
図７は、印字率とトナー付着に起因する反射濃度の変化との関係を示すグラフである。トナー付着量は、原稿の紙サイズによっても異なるので、表２のようにトナー付着量が変化する設定とした。例えば原稿がＡ３サイズで印字率４％の場合は、図７に示すようにトナー付着による反射濃度は０．００８８になる。また、原稿がＡ３サイズなのでトナー付着量係数は、表２に示すように「２」となる。よって、原稿がＡ３サイズのときは、トナー付着による反射濃度は０．００８８×２＝０．０１７６となる。
【表２】

【００７５】
ここで、上述したように温度Ｔ_Ｓで定着ローラ５２や加圧ローラ５４を空回転させて、これらのローラ５２，５４に付着しているトナーに粘度をもたせて記録媒体に転移させることにより除去できるトナー量について説明する。
【００７６】
記録媒体を１０００枚通紙したときの定着ローラ５２の反射濃度が７３．８であった。記録媒体を１０００枚通紙した後、上述した空回転をして白紙１枚を通紙した後では、定着ローラ５２の反射濃度が７４．０となった。従って、上記の空回転によって、反射濃度０．２に相当するトナーを除去できたこととなる。このため、余裕をみてローラの反射濃度が０．０８８になったときに、上記の空回転を行う設定にした。つまり、印字率４％のときは、１枚当たりに反射濃度０．００８８に相当するトナー量がローラに付着するので、１０枚の記録媒体に画像を形成する毎に、上記した空回転をさせればよいこととなる。
【００７７】
上記した第２実施形態では、従来の温度制御を行ったときよりも、定着ローラ５２の表面から加圧ローラ５４に転移するトナーの量を減少できた。しかし、第３実施形態では、原稿の印字率及び記録媒体の枚数に基づいて、各ローラに付着するトナーの量を予測して上記の空回転を行うので、感光ドラム１２や転写ローラ２２の走行距離（回転数）を約１／４程度に減少できる。
【００７８】
上記した従来の温度制御によって印字率４％の原稿で間欠耐久２枚／１０分（１０分間に２枚の記録媒体に画像を形成する）を行う場合、約１５００枚の記録媒体を定着した後では加圧ローラ５４に汚れが発生した。これに対して、第３実施形態の技術を実施したときは、加圧ローラ５４に付着したトナーの量を半分以下に軽減でき、間欠耐久３，０００枚でも加圧ローラ５４にトナー汚れが発生しなかった。
【００７９】
また、上記の第２実施形態と同じようにして、間欠耐久２枚／１０分で１５セット毎に定着ニップ部５８に記録媒体を１０秒停止させ、その後、再起動させる試験でも第２実施形態と同様の結果が得られた。上記したような制御によって定着装置１００の寿命を延ばし、さらには感光ドラム１２や転写ローラ２２の走行距離を１／４に減少できるので、耐久寿命を延ばせた。
【００８０】
図８から図１１までを参照して第４実施形態について説明する。
【００８１】
図８は、第４実施形態の定着装置を示す模式図である。図９は、定着ローラを模式的に示す断面図である。図１０は、定着ローラの厚みと定着ニップ部の温度との関係を示すグラフである。図１１は、定着ローラの表面温度と時間との関係を示すグラフである。図８では、図２に示された構成要素と同一の構成要素には同一の符号が付されている。
【００８２】
上述した第１実施形態から第３実施形態まででは、定着ローラ５２の厚さをｔ＝０．８５ｍｍとした。このため、待機中における定着ニップ部５８の温度を、Ｆｐｏｔが成り立つ最低温度とトナーが最も粘度をもつ温度とが両立する温度にしなければならない。従って、設定する温度範囲が狭くなってしまう。この結果、ハロゲンヒータ５６に供給する電力を高くしたり、定着ローラ５２の厚み公差をできるだけ狭めたりするので、コストが高くなる。
【００８３】
第４実施形態では、図８に示すように、定着装置１１０の定着ローラ１１２の厚さをｔ＝０．３０ｍｍにした。さらに、図９に示すように、定着ローラ１１２の芯金１１５の内部に２本の補強バネ１１６，１１８を挿入した。２本の補強バネ１１６，１１８の巻き方向は、定着ローラ１１２の長手方向中央に向かうように設定されている。これら２本の補強バネ１１６，１１８によって定着ローラ１１２の強度が保たれる。補強バネ１１６，１１８は熱容量に影響しない程度の線径１．０ｍｍ以下であり、且つ、補強バネ１１６，１１８には耐熱黒塗装が施されている。
【００８４】
図９に示すように、芯金１１５の内部に挿入された２本の補強バネ１１６，１１８が巻き方向を定着ローラ１１２の長手方向中央に向かうように設置する理由としては、熱及び加圧ローラ５４の荷重によって補強バネ１１６，１１８がその巻き方向に移動するので、バネの巻き方向が一方向にあると片寄ってしまうからである。ここでは、上記のように２本の補強バネ１１６，１１８が巻き方向を定着ローラ１１２の長手方向中央に向かうように設置した。この結果、補強バネ１１６，１１８は熱及び加圧ローラ５４の荷重によって定着ローラ１１２の長手方向中央に向かう方向に移動しようとするので、補強バネ１１６，１１８が互いに押し合って位置的にバランスがとれる。
【００８５】
また、補強バネ１１６，１１８に耐熱黒塗装を行う。この理由は、補強バネ１１６，１１８自体の熱感度をよくするほか、補強バネ１１６，１１８の表面の摩擦係数を増大させることによって熱及び加圧ローラ５４の荷重によって移動する量を極力減らすためである。
【００８６】
定着ローラ１１２の表層には、離型性をよくするために、フッ素系のＰＴＦＥとＰＦＡ混合樹脂の塗料が塗布されている。また、加圧ローラ５４は、金属製の芯金５４ａの外周面に、シリコーンゴム等の弾性を有する耐熱性の離型層５４ｂを形成した構成である。離型層５４ｂの外周面を下方から定着ローラ１１２に押し付けることにより、定着ローラ１１２と加圧ローラ５４との間に定着ニップ部１１４を形成している。この定着ニップ部１１４の幅は、記録媒体上のトナーを好適に加熱すると共に加圧できる程度に設定されている。
【００８７】
定着ローラ１１２の外周面（表面）にはサーミスタ６０が接触しており、このサーミスタ６０は定着ローラ１１２の外周面の温度を測定する。サーミスタ６０が測定した温度は制御装置６２（ＣＰＵ）に送信される。制御装置６２に送信された温度情報に基づいて、ハロゲンヒータ５６に通電するＡＣ電源（図示せず）のＡＣ電圧をトライアック６４によって位相や周波数制御する。このように制御することにより、ハロゲンヒータ５６に通電する電力を制御して定着ローラ１１２の温度を制御する。この結果、サーミスタ６０が検知した温度が所定の設定温度よりも低いときはハロゲンヒータ５６が昇温するように通電が制御される。一方、サーミスタ６０が検知した温度が所定の設定温度よりも高いときは、ハロゲンヒータ５６が降温するように通電が制御される。このように制御されることにより、定着の際に定着ローラ５２の外周面は一定の温度に調整される。
【００８８】
この第４実施形態の技術では、定着ローラ１１２の肉厚を薄くしたので定着ローラ１１２の熱容量が減る。このため、図１０に示すように、立ち上がり時間（ローラが完全に冷えた状態（室温の状態）から定着温度Ｔ２に昇温するまでの時間）を１／３にできた。また、トナー定着面側に熱容量の小さな定着ローラ１１２を用いることによって、定着ニップ部１１４の熱容量も小さくなる。この結果、トナーに粘度をもたせる温度に定着ニップ部１１４が到達するまでの時間を短縮できると共に、待機中（スタンバイ中）の定着ニップ部１１４の温度が１４０℃から１１０℃までの範囲内の温度になるように制御できる。従って、トナーの分子量分布が高分子側にシフトすることを防ぐことが容易になり、定着ローラ１１２がトナーで汚れにくくなる。このため、定着装置１１０の耐久寿命を延ばせる。また、低温で待機していても立ち上がりが早いため、ハロゲンヒータ５６に供給する電力を大きくする必要もなく、コストダウンを図ることができる。
【００８９】
この第４実施形態の技術では、図１１に示すように、画像形成（プリント）を終了して各ローラが回転を停止してスタンバイに入ったときに、定着ニップ部１１４において定着ローラ１１２及び加圧ローラ５４に付着したトナーが高分子化して固着しないように、トナーが最も粘度をもつ温度（Ｔ１）以下の温度Ｔｓ（１００℃）で温度制御を行う。このため、定着ニップ部１１４は温度Ｔ_Ｓに保たれる。
【００９０】
また、第４実施形態では、熱容量の小さい定着ローラ１１２を使用しているので、スタンバイ温度Ｔ_Ｓが低くても立ち上がり時間が早い。このため、トナー除去前回転制御（定着ニップ部１１４を温度Ｔ１に所定時間保つ制御）が無い場合は、印刷が完了するまでの時間は厚さｔ＝０．８５ｍｍの定着ローラの場合と同等である。使用したトナーは、第１〜第３実施形態で使用したトナーと同じものであるので、トナーが最も粘度をもつ温度Ｔ１は１４０℃である。なお、第４実施形態では、上述した第２及び第３実施形態の温度制御も実施している。
【００９１】
画像形成（印刷）が開始されるに先立って、定着ローラ１１２を回転させない状態で（定着ローラ１１２を停止させたままの状態で）、トナーが最も粘度をもつ温度Ｔ１（１４０℃）に定着ニップ部１１４がなるように、ハロゲンヒータ５６に電力を供給する。定着ニップ部１１４は、スタンバイ温度Ｔ_Ｓから空回転温度Ｔ１までに約２秒で到達する。定着ニップ部１１４が温度Ｔ１に到達した直後から定着ローラ１１２を回転させ始めて、定着ローラ１１２及び加圧ローラ５４に付着しているトナーに粘度をもたせるために８秒間これらのローラを回転させる。その後、定着ニップ部１１４を定着温度Ｔ２（１７５℃）にまで約４秒で昇温させる。定着ニップ部１１４が定着温度Ｔ２（１７５℃）になった後にこの定着ニップ部１１４に記録媒体が到達する（突入する）。
【００９２】
定着ローラ１１２及び加圧ローラ５４に付着したトナーに粘度をもたせる時間は、熱容量の小さな定着ローラ１１２を用いることにより定着ニップ部１１４の熱容量が小さくなったので、図３に示す場合よりも２秒間短縮できた。
【００９３】
記録媒体が定着ニップ部１１４を通過中、定着ローラ１１２と加圧ローラ５４に付着したオフセットトナーは粘度をもったままであるので、このオフセットトナーは離型性の悪い記録媒体に転移して、定着ローラ１１２及び加圧ローラ５４から除去される。記録媒体に転移したオフセットトナーは、蓄積した固着トナーではないので、目には見えない程度のものである。また、厚さｔ＝０．８５ｍｍの定着ローラを使用する場合（図３に示す場合）に比べて定着ローラ１１２の厚さが薄くて熱容量が小さいので、図３の場合に比べて印字開始から排紙完了までの時間を２秒間短縮できた。
【００９４】
画像形成が終了した後は、定着ローラ１１２と加圧ローラ５４は停止する。これらが停止しているときに、定着ニップ部１１４に付着しているトナーが高分子化して固着することがある。そこで、このトナーが固着しないように、トナーが最も粘度をもつ温度（Ｔ１）以下の温度Ｔｓ（ここでは、１００℃）になるように定着ニップ部１１４を保つ。これによりで定着ニップ部１１４においてトナーが固着することを確実に防止できる。
【００９５】
画像形成（プリント）開始毎に、トナーが最も粘度をもつ温度Ｔ１（１４０℃）に定着ニップ部１１４を保った状態で、定着ローラ１１２及び加圧ローラ５４に付着しているトナーに粘度をもたせるために、これらのローラ１１２，５４を８秒間回転させ、その後に定着温度Ｔ２（１７５℃）に定着ニップ部１１４を昇温させる。このように定着ニップ部１１４の温度を制御することにより、定着ローラ１１２及び加圧ローラ５４双方の外周面の全周にわたってトナー汚れを除去できる。これにより各ローラ１１２，５４にトナー等の汚れが蓄積することを防止できる。
【００９６】
本実施形態では、第２実施形態と同じように間欠耐久２枚／１０分で１０セット毎に定着ニップ部１１４に記録媒体を１０秒間停止させてから再起動させる試験を行った場合、第２実施形態と同様の結果が得られた。
【００９７】
上記のように定着ニップ部１１４の温度を制御することにより、定着装置１１０の寿命を延ばし、さらに、感光ドラムや転写ローラの走行距離を１／４程度に減少させることができる。このため、定着装置１１０の耐久寿命を延ばすことが可能となり、また、印字開始から排紙完了までの時間を短縮できるので、エネルギー消費効率も３０％程度下げることができた。
【００９８】
【発明の効果】
以上説明したように本発明の定着装置によれば、一対の定着回転体にトナーが付着していても、この一対の定着回転体が停止中（待機中）は、定着ニップ部が所定の最高粘度温度以下の温度になるように加熱手段が制御されるので、一対の定着回転体に付着しているトナーは高分子化せずにこの定着回転体に固着しない。また、定着ニップ部に記録媒体を挟持しながら搬送する（定着する）に先立って、定着ニップ部を最高粘度温度にして空回転させるので、一対の定着回転体に付着しているトナーが高い粘性をもつ（高粘度のトナーになる）。その後、定着温度で定着を開始するので、高粘度のトナーは、離型性の悪い記録媒体に転移する（オフセットする）。従って、一対の定着回転体にトナーがほとんど蓄積しない。なお、一対の定着回転体にはトナーがほとんど蓄積しないので、記録媒体に転移したトナーは目に見えない程度の微量である。
【００９９】
ここで、前記一対の定着回転体は、前記定着ニップ部に記録媒体を挟持しながら搬送するに先立って前記一対の定着回転体が前記空回転するときには、１０秒間以上１５秒間以下の範囲内の時間だけ空回転するものである場合は、一対の定着回転体に付着しているトナーが高い粘性をいっそう確実にもつので、これらのトナーは記録媒体にいっそう確実に転移する。この結果、一対の定着回転体にトナーがいっそう確実にほとんど蓄積しない。
【０１００】
また、前記所定の最高粘度温度は、前記一対の定着回転体の前記定着ニップ部に所定量のトナーを入れて前記一対の定着回転体を回転させたときに、このトナーが前記一対の定着回転体の間で最も糸を引く温度である場合は、トナーがいっそう確実に最高の粘性を発揮する。
【０１０１】
さらに、前記定着ニップ部に記録媒体を挟持しながら搬送している際に前記一対の定着回転体が停止した場合において、この一対の定着回転体を再び回転させて定着を開始するときは、この定着を開始するに先立って、前記最高粘度温度で前記一対の定着回転体を所定時間だけ空回転させ、その直後に、前記定着ニップ部を前記定着温度に昇温してクリーニング用の記録媒体を該定着ニップ部で挟持しながら搬送する場合は、定着ニップ部に記録媒体を挟持しながら搬送している際に一対の定着回転体が停止することにより一対の定着回転体にトナーが付着することがあるが、定着を再開するに先立って、上記の空回転とクリーニング用の記録媒体を搬送するので、一対の定着回転体に付着しているトナーはクリーニング用の記録媒体に転移する。このため、一対の定着回転体にトナーがほとんど蓄積しない。
【０１０２】
さらにまた、前記定着ニップ部に記録媒体を挟持しながら搬送するに先立って前記定着ニップ部に記録媒体を挟持せずに前記一対の定着回転体が空回転する動作は、印字率に基づいて行うものである場合は、所定の印字率よりも少ないときは空回転させずに、所定の印字率を超えたときに空回転させることにより、空回転の回数が減少するので、一対の定着回転体の摩耗を抑制できる。
【０１０３】
さらにまた、前記最高粘度温度が１２０℃以上１５０℃以下の範囲内のトナーを記録媒体に定着する場合は、最高粘度温度を１２０℃以上１５０℃以下の範囲内に設定できる。
【０１０４】
さらにまた、前記一対の定着回転体のうちのいずれか一方は、この一方の定着回転体を補強する補強バネがその内部に挿入されたものである場合は、一対の定着回転体のうちの一方の肉厚を薄くできるので、定着ニップ部の温度を制御し易い。
【０１０５】
また、本発明の画像形成装置によれば、トナー汚れの無い良好な画像を記録媒体に形成できる。
【図面の簡単な説明】
【図１】本発明の定着装置の一実施形態が組み込まれた画像形成装置の一例であるレーザビームプリンタを示す模式図である。
【図２】定着装置を模式的に示す側面図である。
【図３】定着ローラ表面温度の制御を示すグラフである。
【図４】トナーの粘度を測定するための装置を示す模式図である。
【図５】第３実施形態の定着装置を示す模式図である。
【図６】予測付着トナーを示すグラフである。
【図７】印字率とトナー付着に起因する反射濃度の変化との関係を示すグラフである。
【図８】第４実施形態の定着装置を示す模式図である。
【図９】定着ローラを模式的に示す断面図である。
【図１０】定着ローラの厚みと定着ニップ部の温度との関係を示すグラフである。
【図１１】定着ローラの表面温度と時間との関係を示すグラフである。
【符号の説明】
５０，１１０ 定着装置
５２，１１２ 定着ローラ
５４ 加圧ローラ
５６ ハロゲンヒータ
５８ 定着ニップ部
６０ サーミスタ
６２ 制御装置[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention incorporates a fixing device that fixes a toner image to a recording medium by nipping and conveying the recording medium to a fixing nip formed by pressing a pair of fixing rotators against each other, and the fixing device is incorporated. To an image forming apparatus.
[0002]
[Prior art]
2. Description of the Related Art As an output device of a computer or a workstation, an electrophotographic image forming apparatus that forms an image on a recording medium using a powder developer (toner) is known. In such an image forming apparatus, for example, an image carrier such as a photosensitive drum is irradiated with light (for example, laser light) carrying image information to form an electrostatic latent image, and a developing roller is applied to the electrostatic latent image. Is used to form a developed image, and the developed image is transferred to a recording medium using a transfer roller or the like to form a transferred image (developed image). The recording medium on which the transfer image has been formed is transported to a fixing device, where the transfer image is fixed on the recording medium. The fixing device includes, for example, a fixing roller having a built-in heater and a pressure roller that is in pressure contact with the fixing roller. When fixing the transferred image on the recording medium, the transferred image is heated at a predetermined fixing temperature while being conveyed while nipping and transporting the recording medium between a fixing roller and a pressure roller, and at the same time, pressure is applied. The transferred image is fixed on the recording medium by the heating and the pressing. The recording medium on which the transfer image is fixed is discharged while being nipped by a discharge roller or the like.
[0003]
Recently, an aluminum alloy has been used as the core of the fixing roller to reduce its thickness to about 0.25 mm to 0.30 mm, and at the same time, ribs have been formed inside the core or a reinforcing member has been inserted. Or By using the fixing roller having such a configuration, it is possible to shorten the time for raising the fixing roller from the standby state to the fixing temperature (start-up time), thereby improving operability.
[0004]
As the fixing device, in addition to the heat roller method using the fixing roller described above, a film heat fixing method is employed. The fixing device of the film heat fixing method includes a cylindrical thin film having a heating element disposed therein and rotating in the circumferential direction thereof, and a pressure roller rotating in the circumferential direction while being pressed against the thin film. The recording medium is conveyed while being sandwiched between the thin film and the pressure roller to fix a developed image on the recording medium.
[0005]
In such a film heat fixing type fixing device, a ceramic heater can be used as an internal heating element. The ceramic heater has a basic configuration including, for example, an insulating and good heat conductive ceramic base material, which is a material having a high temperature and a low heat capacity, and a resistance heating layer formed on the surface of the ceramic base material. Things.
[0006]
Further, in the fixing device of the film heat fixing method, a thin film material having a low heat capacity can be used as the film material, and since the temperature of the film material is increased in a short period of time, power is supplied to the film material during standby. No need to do. Further, even if the recording medium is passed immediately, the film material can be heated to the fixing temperature before the recording medium reaches the fixing nip portion, so that the wait time can be shortened (quick start property: operates on demand). ) And power saving.
[0007]
In the fixing device of the film heat fixing system, it is not necessary to supply electric power to the film material during standby as described above, so that the temperature inside the image forming apparatus main body can be suppressed from rising. On the other hand, in the fixing device of the film heat fixing system, the recording medium is conveyed by driving the pressure roller, but the outer diameter of the pressure roller may fluctuate due to thermal expansion. For this reason, in order to keep the conveyance speed of the recording medium constant, it is necessary to control the rotation speed of the pressure roller, so that there is a problem that the cost increases.
[0008]
By the way, it is ideal that all the unfixed toner (developed image) carried on the surface of the recording medium is appropriately heated and melted and fixed on the surface of the recording medium. However, a toner in a cold offset state that cannot be completely melted and a toner in a hot offset state that has been melted too much exist on the recording medium in the fixing nip portion. These toners may transfer to a fixing roller or a fixing film in contact with the surface of the recording medium. Further, there is a case where the toner is electrostatically offset on the fixing roller or the fixing film. As described above, the toner transferred to the fixing roller or the fixing film may be transferred to the pressure roller between papers (between recording media passing through the fixing nip). As a result, the toner adheres to the fixing roller, the fixing film, or the pressure roller, and the toner is contaminated.
[0009]
If toner stains continue to occur on the fixing roller, fixing film, or pressure roller, toner (toner stains) accumulates on the fixing roller and the like. In order to prevent this accumulation, the surface layers of the fixing roller, the fixing film, and the pressure roller are generally provided with fluororesin layers such as PTFE, PFA, and FEP, LTV, A release layer made of a silicone rubber layer such as an RTV is provided. Further, a cleaning member such as a web or a cleaning roller may be provided in order to collect toner adhered to the surface layer of the fixing roller, the fixing film, and the pressure roller.
[0010]
[Problems to be solved by the invention]
However, a toner release layer such as a fluorine-containing resin used as a surface layer of the above-described fixing roller, fixing film, and pressure roller cannot completely eliminate toner contamination.
[0011]
The fixing roller and the fixing film are always heated to the toner melting temperature during image formation. Therefore, the toner adhering to the surface of the fixing roller or the fixing film is in a molten state. Therefore, when the recording medium to be fixed next reaches the fixing nip portion, the toner image on the surface of the recording medium and the toner melted on the surface of the fixing roller and the like are mixed and move to the recording medium. , Or to the pressure roller between sheets. As a result, the fixing roller and the fixing film are not continuously stained with the toner.
[0012]
On the other hand, toner stains generated on the fixing roller or the fixing film are transferred to the pressure roller. Since the temperature of the pressure roller is lower than that of the fixing roller or the fixing film, the toner stain transferred to the pressure roller does not always exist in a completely melted state on the pressure roller. Further, since the toner image on the surface of the recording medium does not come into contact with the pressure roller, toner dirt rarely mixes with the toner image, and once toner dirt is generated, the toner dirt accumulates.
[0013]
When toner stains accumulate on the pressure roller, the releasability of the pressure roller decreases. For this reason, the recording medium (especially when the recording medium is an OHP film) may be wound around the pressure roller, or the accumulated toner stains may stain the recording medium at once.
[0014]
Further, due to the above-mentioned phenomenon, in a heat roller type fixing device, toner fouling occurs on the fixing roller. In a fixing device of a heat roller type, in order to shorten a first printout time (hereinafter, FPOT), the temperature of the fixing roller is controlled to a predetermined temperature during standby (standby). When toner contamination occurs on the pressure roller, the molecular weight distribution of the toner may shift to the polymer side due to heat and pressure at the fixing nip formed by the fixing roller and the pressure roller. This causes a phenomenon in which the toner sticks to the fixing roller that generates heat and sticks.
[0015]
By the way, recently, electrophotographic printers are widely used all over the world, and accordingly, recording media used in the printers have been diversified. For example, in the European market, a recording medium having high rigidity and high whiteness is preferred, and CaCo is used as a filler for the recording medium. ₃ Is often used.
[0016]
However, CaCo ₃ When the toner adheres to the pressure roller, the releasability of the pressure roller is deteriorated, and the toner contamination on the pressure roller is accelerated and further deteriorated. This CaCO ₃ The extent to which the particles adhere to the pressure roller becomes more severe in a low humidity environment. Further, the toner contamination of the pressure roller becomes more severe in a low humidity environment. For example, in an environment of a temperature of 15 ° C. and a humidity of 10%, CaCO ₃ When a paper-passing durability test is performed using a recording medium containing 10 to 15%, toner contamination starts to occur on the pressure roller when the number of sheets passed from 1,000 to 2,000. With approximately the same number of sheets, toner contamination occurs on the recording medium, resulting in an image defect. In addition, there is a method of installing a cleaning member in order to prevent roller contamination. However, it is necessary to regularly replace the product cost and the cleaning member, so that the running cost is also increased.
[0017]
In view of the above circumstances, it is an object of the present invention to provide a fixing device in which toner hardly accumulates on a fixing rotating body such as a fixing roller and a pressure roller, and an image forming apparatus incorporating the fixing device.
[0018]
[Means for Solving the Problems]
To achieve the above object, the fixing device of the present invention is a fixing nip formed by pressing a pair of fixing rotators against each other, by transporting a recording medium carrying an unfixed toner image while nipping the recording medium. In a fixing device for fixing a toner image on the recording medium,
(1) heating means for heating the fixing nip portion;
(2) temperature control means for controlling the temperature of the heating means,
(3) The temperature control means includes:
(3-1) While the pair of fixing rotators are stopped, the heating unit is controlled so that the fixing nip portion is at a temperature equal to or lower than a predetermined maximum viscosity temperature, and
(3-2) when the pair of fixing rotators rotate idly without holding the recording medium in the fixing nip section before the recording medium is conveyed while pinching the recording medium in the fixing nip section, Control the heating means so that the highest viscosity temperature, then,
(3-3) When the recording medium is conveyed while nipping the fixing nip portion, the heating means is controlled so that the fixing temperature is higher than the maximum viscosity temperature. Is what you do.
[0019]
here,
(4) The pair of fixing rotators may rotate within a range of 10 seconds or more and 15 seconds or less when the pair of fixing rotators rotate idle before the recording medium is conveyed while nipping the recording medium between the fixing nip portions. It may rotate idle for the time.
[0020]
Also,
(5) The predetermined maximum viscosity temperature is such that when a predetermined amount of toner is put in the fixing nip portion of the pair of fixing rotators and the pair of fixing rotators are rotated, the toner is fixed to the pair of fixing rotators. The temperature at which the yarn is pulled most between the rotating bodies may be used.
[0021]
further,
(6) When the pair of fixing rotators are stopped while the recording medium is being conveyed while nipping the fixing nip portion, when the pair of fixing rotators are rotated again to start fixing, Prior to the start of the fixing, the pair of fixing rotators are idlely rotated for a predetermined time at the maximum viscosity temperature, and immediately thereafter, the fixing nip is heated to the fixing temperature and the recording medium for cleaning is rotated. May be conveyed while being pinched by the fixing nip portion.
[0022]
Furthermore,
(7) The operation in which the pair of fixing rotators rotate idly without holding the recording medium in the fixing nip portion before the recording medium is conveyed while pinching the recording medium in the fixing nip portion is performed based on a printing rate. You may.
[0023]
Furthermore,
(8) The toner having the maximum viscosity temperature in the range of 120 ° C. or more and 150 ° C. or less may be fixed on a recording medium.
[0024]
Furthermore,
(9) One of the pair of fixing rotators may have a reinforcing spring for reinforcing the one fixing rotator inserted therein.
[0025]
Further, an image forming apparatus of the present invention for achieving the above object,
(10) An image carrier on which a toner image is formed, a transfer device for transferring the toner image to a recording medium, and the fixing device described above.
[0026]
BEST MODE FOR CARRYING OUT THE INVENTION
The schematic structure of an image forming apparatus in which an embodiment of the fixing device of the present invention is incorporated will be described with reference to FIG.
[0027]
FIG. 1 is a schematic diagram showing a laser beam printer as an example of an image forming apparatus in which an embodiment of the fixing device of the present invention is incorporated.
[0028]
The laser beam printer 10 includes a photosensitive drum 12 that is rotated in a direction indicated by an arrow A at a predetermined process speed by a drive motor (not shown). The photosensitive drum 12 is irradiated with a laser beam 14 carrying image information from a scanner 16 to form an electrostatic latent image.
[0029]
Around the photosensitive drum 12, a charging roller 18 for uniformly charging the surface layer of the photosensitive drum 12 and an electrostatic latent image formed on the photosensitive drum 12 are substantially sequentially arranged along the rotation direction (the direction of arrow A). A developing device 20 for supplying a developer, a transfer roller 22 for transferring a developed image formed on the photosensitive drum 12 to a recording medium, and a cleaning device 24 for removing the developer remaining on the photosensitive drum 12 are provided.
[0030]
A paper feed cassette 26 for accommodating a sheet-like recording medium such as recording paper is detachably mounted below the laser beam printer 10. The recording medium is fed from a paper feed cassette 26 by a paper feed roller 28 in a predetermined paper feed direction (arrow B direction). A transport roller 30, a top sensor 32, a transport guide 34, a fixing device 50, a transport roller 36, and a paper discharge roller 38 are arranged in this order from the upstream side to the downstream side in the paper feeding direction.
[0031]
A procedure for forming an image by the laser beam printer 10 will be described.
[0032]
A laser beam 14 carrying image information is emitted from the scanner 16 to the photosensitive drum 12 to form an electrostatic latent image. The electrostatic latent image is developed with the developer supplied from the developing device 20 to form a developed image on the photosensitive drum 12.
[0033]
On the other hand, a recording medium is fed from a sheet feeding cassette 26 in a direction of arrow B (sheet feeding direction) by a sheet feeding roller 28, and is conveyed to a transfer roller 22 by a conveying roller 30. The transfer roller 22 transfers the developed image of the photosensitive drum 12 to the recording medium while sandwiching the recording medium with the photosensitive drum 12. The recording medium on which the developed image has been transferred is guided to the fixing device 50 by the transport guide 34. The fixing device 50 is provided with a fixing roller 52 and a pressure roller 54. The recording medium is conveyed while being nipped between these two rollers 52 and 54, and the developed image is fixed on the recording medium. The recording medium on which the developed image has been fixed in this manner is discharged by the discharge roller 38 and stacked on the discharge tray 40.
[0034]
The fixing device 50 will be described with reference to FIG.
[0035]
FIG. 2 is a side view schematically illustrating the fixing device.
[0036]
The fixing device 50 includes a fixing roller 52 having a built-in halogen heater 56 (an example of a heating unit according to the present invention), and a pressure roller 54 pressed against the fixing roller 52. As the fixing roller 52, a roller in which the outer peripheral surface of a cored bar 52a (0.85 mm thick) made of, for example, a pipe member made of iron or aluminum is coated with a fluororesin layer 52b having good releasability is used. The fixing roller 52 is rotated in the direction of arrow C by a driving source (not shown). The fixing roller 52 and the pressure roller 54 are examples of a pair of fixing rotators according to the present invention.
[0037]
The pressure roller 54 is for pressing the recording medium 11 against the fixing roller 52 with a predetermined pressure. As the pressure roller 54, a roller in which an outer peripheral surface of a metal core metal 54a is coated with an elastic layer 54b made of, for example, silicone rubber or fluorine rubber to a predetermined thickness is used. While pressing the pressure roller 54 against the fixing roller 52 at a predetermined pressure and rotating the fixing roller 52 in the direction of arrow C, a load for fixing the toner 11a to the recording medium 11 is applied.
[0038]
A portion where the fixing roller 52 and the pressure roller 54 are in contact is a fixing nip portion 58, and the width of the fixing nip portion 58 is set so that the toner 11a on the recording medium 11 can be accurately heated and pressed. Have been.
[0039]
The thermistor 60 is in contact with the outer peripheral surface (front surface) of the fixing roller 52, and measures the temperature of the outer peripheral surface of the fixing roller 52. The temperature measured by the thermistor 60 is transmitted to the control device 62 (CPU, which is an example of a temperature control unit according to the present invention). Based on the temperature information transmitted to the control device 62, the phase and frequency of the AC voltage of an AC power supply (not shown) for supplying electricity to the halogen heater 56 are controlled by the triac 64. By controlling in this manner, the power supplied to the halogen heater 56 is controlled to control the temperature of the fixing roller 52. As a result, when the temperature detected by the thermistor 60 is lower than a predetermined set temperature, the energization is controlled so that the halogen heater 56 is heated. On the other hand, when the temperature detected by the thermistor 60 is higher than a predetermined set temperature, the energization is controlled so that the temperature of the halogen heater 56 decreases. With such control, the outer peripheral surface of the fixing roller 52 is adjusted to a constant temperature at the time of fixing.
[0040]
When the recording medium 11 enters the fixing nip 58, the toner 11 a on the recording medium 11 melts at a predetermined fixing temperature, and the molten toner 11 a is pressed against the recording medium 11 by the pressing force of the pressure roller 54. And is fixed to the recording medium 11. The recording medium 11 on which the toner 11a is fixed is separated from the fixing roller 52 and the pressure roller 54 by separation claws (not shown) and reaches a paper discharge roller 38 (see FIG. 1). Is discharged.
[0041]
A first embodiment in which the temperature of the fixing heater 58 is varied by controlling the temperature of the halogen heater 56 will be described.
[0042]
In the conventional temperature control, the power of the laser beam printer 10 is turned on, but when the toner is not fixed on the recording medium by the fixing device 50 (during standby), the temperature of the fixing nip portion 58 (fixing roller 52 is controlled so as to become the fixing temperature (here, 175 ° C.). In the case of such control, the fixing nip portion 58 is in a state where a load is applied at a high temperature. In such a state, of the toner adhering to the surfaces of the fixing roller 52 and the pressure roller 54, the toner sandwiched between the fixing nip portions 58 polymerizes and adheres to the fixing roller 52 on the heat source side. I do. Due to the fixed toner, the releasability of the surface of the fixing roller 52 is deteriorated, and the toner stain is increased. Further, part of the toner adhered to the surface of the fixing roller 52 or the pressure roller 54 is transferred to the recording medium every printing. However, since the amount of accumulated toner is larger than the amount of toner transferred to the recording medium, toner smearing is promoted.
[0043]
Therefore, the temperature of the fixing nip 58 is controlled as described below so as not to accumulate the toner adhered to the fixing roller 52 and the pressure roller 54. This control will be described with reference to FIG.
[0044]
FIG. 3 is a graph showing control of the fixing roller surface temperature. The vertical axis represents the surface temperature of the fixing roller 52 (the temperature of the fixing nip), and the horizontal axis represents time (second).
[0045]
In the laser beam printer 10, when image formation (printing) is completed, the fixing roller 52 and the pressure roller 54 stop rotating and are in a standby state. During this standby period, a temperature lower than the temperature at which the toner has the highest viscosity (maximum viscosity temperature) so that the toner adhering to the fixing roller 52 and the pressure roller 54 is not polymerized and fixed in the fixing nip portion 58. The temperature of the halogen heater 56 is controlled so that the fixing nip 58 is formed at Ts. In the present embodiment, the temperature T1 (140 ° C.) at which the toner has the highest viscosity is set to Ts in order to shorten the time from standby to completion of printing.
[0046]
When printing is started, the fixing roller 52 and the pressure roller 54 are rotated idle (pre-rotation) prior to the start of printing. During this idle rotation, the temperature of the halogen heater 56 is controlled so that the fixing nip 58 is at a temperature T1 (140 ° C.) where the toner has the highest viscosity. In a state where the temperature of the fixing nip portion 58 is maintained at the temperature T1, the rollers 52 and 54 are pressed for 10 seconds to 15 seconds in order to soften the toner adhered to the fixing roller 52 and the pressure roller 54. Just rotate.
[0047]
Thereafter, the halogen heater 56 is controlled so that the temperature of the fixing nip 58 becomes the fixing temperature (printing temperature T2 (175 ° C.)). Six seconds after the start of this control, the recording medium enters the fixing nip 58 (begins to be pinched). In this state, the toner (offset toner) adhering to the fixing roller 52 and the pressure roller 54 has a viscosity, and the offset toner is transferred from the fixing roller 52 and the pressure roller 54 while the recording medium passes through the fixing nip 58. Transfer to a recording medium with poor releasability. Since the offset toner transferred to the recording medium is not the fixed toner that has accumulated, it is invisible to the naked eye.
[0048]
After the printing is completed, the fixing nip portion 58 is set at a temperature Ts (140 ° C. in this case) equal to or lower than the temperature at which the toner has the highest viscosity so that the molecular weight distribution of the toner located in the fixing nip portion 58 does not become high. Thus, the halogen heater 56 is controlled. As a result, the toner does not adhere to the fixing roller 52.
[0049]
Prior to each start of printing, the halogen heater 56 is controlled so that the fixing nip 58 is at a temperature T1 at which the toner has the highest viscosity. In this case, the fixing roller 52 and the pressure roller 54 are rotated for 10 seconds so that the toner adhered to the fixing roller 52 and the pressure roller 54 has viscosity. Thereafter, the temperature of the fixing nip 58 is raised to the fixing temperature T2 (175 ° C.). As a result, toner contamination can be removed over the entire outer peripheral surfaces of the fixing roller 52 and the pressure roller 54. As a result, toner contamination hardly accumulates on the fixing roller 52 and the pressure roller 54.
[0050]
The temperature at which the toner has the highest viscosity (the highest viscosity temperature) will be described with reference to FIG.
[0051]
FIG. 4 is a schematic diagram showing an apparatus for measuring the viscosity of the toner.
[0052]
This device 80 includes a heating roller 82 having an outer diameter of 30 mm and a pressing roller 84 having an outer diameter of 25 mm. The pressing roller 84 is pressed against the heating roller 82 by a coil spring 86 at a total pressure of 10 kgf. A halogen heater 88 is arranged inside the heating roller 82. The temperature detecting element 90 is in contact with the outer peripheral surface of the heating roller 82. The temperature control board 92 controls the temperature of the halogen heater 88 based on the temperature detected by the temperature detecting element 90. Thus, the surface temperature of the heating roller 82 is appropriately controlled. To obtain the highest viscosity temperature, 1 g of the toner was put between the heating roller 82 and the pressure roller 84 (nip portion) and heated at an arbitrary temperature. The maximum viscosity temperature was defined as the temperature at which the toner was drawn in a thread form at the nip. This temperature varies depending on the physical properties of the toner and the like.
[0053]
The surface 82a of the heating roller 82 is coated with a PTFE fluororesin having good releasability. The pressure roller 84 is formed by providing a heat-resistant release layer 84b having elasticity such as silicone rubber on the outer peripheral surface of a metal core 84a.
[0054]
Table 1 shows the results described above.
[Table 1]

[0055]
As shown in Table 1, the temperature T1 at which the toner of the present embodiment has the highest viscosity was set to 140 ° C. since 140 ° C. became the most thread-like state.
[0056]
Conventional temperature control (control of setting the temperature of the fixing nip portion 58 to a fixing temperature (here, 175 ° C. during standby)) is performed, and intermittent durability (here, 10 minutes) is applied to a document having a printing rate of 4%. (Image formation on two recording media). In this case, toner contamination occurred on the pressure roller 54 when an image was formed on about 1500 recording media.
[0057]
On the other hand, the temperature of the fixing nip 58 is controlled to the temperature Ts (140 ° C. in this case) during standby and then the temperature of the fixing nip 58 during idling (pre-rotation). In T1 (here, a technique of controlling the temperature to 140 ° C.), the amount of toner adhering to the pressure roller 54 can be reduced to half or less. No toner contamination occurred on the sample No. 54. Further, according to the technology of the present embodiment, even if the surface coats of the fixing roller 52 and the pressure roller 54 vary, it is possible to effectively prevent toner from adhering to each roller. There is no need to achieve high precision. Therefore, it is possible to reduce the cost by improving the yield.
[0058]
A second embodiment in which the temperature of the halogen heater 56 is controlled to change the temperature of the fixing nip 58 will be described.
[0059]
In the case of forming an image while controlling the temperature as in the first embodiment, the fixing roller 52 and the pressure roller 54 may stop when the laser beam printer 10 detects an abnormality while the recording medium passes through the fixing nip 58. There is. In this case, a large amount of toner adheres to the fixing roller 52 and the pressure roller 54 in the fixing nip 58 because the recording medium is still held between the fixing nip 58. After the fixing roller 52 and the pressure roller 54 resume rotation, a certain amount of toner is transferred to the first recording medium that passes through the fixing nip 58. However, most of the toner remains on the fixing roller 52 or the pressure roller 54. For this reason, in the case of continuous printing, the toner remaining on the surface of the fixing roller 52 or the pressure roller 54 has a reduced releasability, so that the offset state on the image may continue for a long time.
[0060]
According to the technology of the second embodiment, even when the fixing roller 52 and the pressure roller 54 stop due to the abnormality detection of the laser beam printer 10 while the recording medium is passing through the fixing nip 58, the fixing roller 52 And the toner hardly accumulates on the surface of the pressure roller 54.
[0061]
A second embodiment will be described.
[0062]
In the second embodiment, a fixing device 50 having the same configuration as that of the first embodiment is used.
[0063]
When the laser beam printer 10 detects an abnormality while the recording medium 11 passes through the fixing nip 58, the fixing roller 52 and the pressure roller 54 stop. Thereafter, when fixing is restarted, the fixing roller 52 and the pressure roller 54 are idled. During the idle rotation, the halogen heater 56 is controlled such that the temperature of the fixing nip 58 becomes the temperature T1 (140 ° C.) at which the toner has the highest viscosity. In this state, the fixing roller 52 and the pressure roller 54 are idled for only 10 to 15 seconds. Immediately after this idle rotation, the halogen heater 56 is controlled so that the fixing nip 58 becomes the fixing temperature T2 in about 6 seconds, and one sheet of white paper (an example of a recording medium for cleaning) passes through the fixing nip 58. Let it.
[0064]
A large amount of toner adhering to the fixing roller 52 and the pressure roller 54 is transferred to the above-mentioned one white sheet. As a result, an image without offset toner can be obtained during actual printing. Further, by removing the toner adhered to the fixing roller 52 and the pressure roller 54, the durability of these rollers 52 and 54 is also improved.
[0065]
Here, using a document having a stamping rate of 4%, the intermittent durability 2 sheets / 10 minutes (image formation on two sheets of recording medium in 10 minutes) is set as one set, and the recording medium is stored in the fixing nip portion 58 every 15 sets. Was stopped for 10 seconds and then restarted.
[0066]
In the conventional temperature control described above (when the power of the laser beam printer 10 is turned on, but the toner is not fixed on the recording medium by the fixing device 50 (during standby), the temperature of the fixing nip 58 is fixed. When a test was performed at a temperature (here, 175 ° C.) (hereinafter, this control is referred to as conventional temperature control), toner contamination occurred on the pressure roller 54 on about 500 sheets. On the other hand, according to the technique of the second embodiment, the amount of toner adhering to the pressure roller 54 can be reduced to half or less, and no toner stain occurs even with 4000 sheets of intermittent durability.
[0067]
A third embodiment will be described.
In the above-described first and second embodiments, the toner adhered to the fixing roller 52 and the pressure roller 54 is given an adhesive property during idle rotation (pre-rotation) and transferred to the recording medium. By doing so, dirt such as toner and paper dust adhering to these rollers 52 and 54 was suppressed. As a result, the durability life of the fixing device 50 can be extended. In addition, the contamination of the fixing roller 52 and the pressure roller 54 was considerably reduced.
[0068]
However, if the pre-rotation is performed for 10 seconds each time printing is performed and each time the start-up operation is returned after stopping, the photosensitive drum 12 and the transfer roller 22 are worn, and the durability is reduced. Further, since the time from the start of printing to the completion of paper ejection is long, power saving is disadvantageous and usability is deteriorated.
[0069]
Therefore, a technique for solving these will be described with reference to FIG.
[0070]
FIG. 5 is a schematic diagram illustrating a fixing device according to a third embodiment. In this figure, the same components as those shown in FIG. 2 are denoted by the same reference numerals.
[0071]
In the fixing device 100 according to the third embodiment, a printing rate calculation device 102 (CPU) is added to the fixing device 50 according to the first embodiment. The printing ratio calculation device 102 calculates the ratio (printing ratio) of the image to the entire surface area of the document. The toner adhering to the fixing roller 52 and the pressure roller 54 is predicted from the printing rate per original document calculated by the printing rate calculation device 102. When the estimated amount of the adhered toner exceeds a predetermined amount, the control device 62 controls the halogen heater 56 so that the fixing nip portion 58 is brought to the temperature T1 (140 ° C.) where the toner has the highest viscosity. And the pressure roller 54 is idled for only 10 seconds. After the idle rotation, the control device 62 starts controlling the halogen heater 56 so that the fixing nip 58 becomes the fixing temperature T2 (175 ° C.), and the recording medium is conveyed to the fixing nip 58 six seconds later.
[0072]
With reference to FIG. 6, the estimation of the amount of toner adhering to the fixing roller and the pressure roller will be described. FIG. 6 is a graph showing the predicted adhesion toner. The estimated amount of adhered toner in this figure is based on a thick paper basis weight of 80 g / m2 in order to predict the printing rate, the toner concentration, and the amount adhered to the pressure roller. ² And cangas paper having poor surface properties was used. Using such a recording medium, an image is continuously formed on 1000 sheets of the recording medium from a state in which the fixing roller 52 and the pressure roller 54 are completely cooled. The dirt was collected with a transparent tape (Mylar tape), and the reflection density (REFLECOMETER MODEL TC-6DS manufactured by Tokyo Denshoku) was measured. The amount of the attached toner was estimated from the reflection density.
[0073]
As a result of measuring the reflection density in this manner, it was found that, in the case of a document having a printing rate of 4%, toner equivalent to a reflection density of about 0.0088 per document continued to adhere to the roller and increased. Further, in the case of a document having a printing ratio of 40%, it was found that toner corresponding to a reflection density of about 0.0129 per document continued to adhere to the roller and increased. Therefore, when the printing rate increases by a factor of 10, the amount of toner adherence increases by a factor of approximately 1.5. From this experiment, the settings of the printing rate and the toner adhesion amount per sheet were set as shown in FIG.
[0074]
FIG. 7 is a graph showing a relationship between a printing rate and a change in reflection density caused by toner adhesion. Since the toner adhesion amount varies depending on the paper size of the document, the setting is such that the toner adhesion amount changes as shown in Table 2. For example, when the original is A3 size and the printing rate is 4%, the reflection density due to toner adhesion is 0.0088 as shown in FIG. Further, since the original is A3 size, the toner adhesion coefficient is “2” as shown in Table 2. Therefore, when the document is A3 size, the reflection density due to toner adhesion is 0.0088 × 2 = 0.0176.
[Table 2]

[0075]
Here, as described above, the temperature T _S Next, the amount of toner that can be removed by causing the fixing roller 52 and the pressure roller 54 to idle and causing the toner adhering to these rollers 52 and 54 to have viscosity and transfer to the recording medium will be described.
[0076]
The reflection density of the fixing roller 52 when 1,000 sheets of the recording medium were passed was 73.8. After passing one thousand sheets of recording medium and then passing one blank sheet by performing the above-described idle rotation, the reflection density of the fixing roller 52 became 74.0. Therefore, the toner corresponding to the reflection density of 0.2 can be removed by the idle rotation. For this reason, when the reflection density of the roller becomes 0.088 with a margin, the above idle rotation is set. That is, when the printing rate is 4%, the toner amount corresponding to the reflection density of 0.0088 per sheet adheres to the roller. Therefore, every time an image is formed on ten recording media, the idle rotation is performed. That is all you need to do.
[0077]
In the above-described second embodiment, the amount of toner transferred from the surface of the fixing roller 52 to the pressing roller 54 can be reduced as compared with the case where the conventional temperature control is performed. However, in the third embodiment, the idling is performed by estimating the amount of toner adhering to each roller based on the printing ratio of the document and the number of recording media. The distance (the number of rotations) can be reduced to about 1/4.
[0078]
In the case of performing intermittent durability 2 sheets / 10 minutes (image formation on 2 sheets of recording medium in 10 minutes) with a document having a printing rate of 4% by the above-described conventional temperature control, after fixing about 1500 sheets of recording medium Thus, the pressure roller 54 was stained. On the other hand, when the technology of the third embodiment is implemented, the amount of toner adhering to the pressure roller 54 can be reduced to less than half, and toner contamination occurs on the pressure roller 54 even with 3,000 sheets of intermittent durability. Did not.
[0079]
In the same manner as in the above-described second embodiment, the recording medium is stopped in the fixing nip unit 58 for every 15 sets at intervals of 2 sets / 10 minutes, and then restarted, and then restarted. The same result as was obtained. With the above-described control, the life of the fixing device 100 can be extended, and the traveling distance of the photosensitive drum 12 and the transfer roller 22 can be reduced to ４, so that the durability life can be extended.
[0080]
The fourth embodiment will be described with reference to FIGS.
[0081]
FIG. 8 is a schematic diagram illustrating a fixing device according to a fourth embodiment. FIG. 9 is a cross-sectional view schematically illustrating the fixing roller. FIG. 10 is a graph showing the relationship between the thickness of the fixing roller and the temperature of the fixing nip. FIG. 11 is a graph showing the relationship between the surface temperature of the fixing roller and time. 8, the same components as those shown in FIG. 2 are denoted by the same reference numerals.
[0082]
In the first to third embodiments described above, the thickness of the fixing roller 52 is set to t = 0.85 mm. For this reason, the temperature of the fixing nip 58 during standby must be a temperature at which the lowest temperature at which Fpot is satisfied and the temperature at which the toner has the highest viscosity are compatible. Therefore, the set temperature range becomes narrow. As a result, the power supplied to the halogen heater 56 is increased, and the thickness tolerance of the fixing roller 52 is reduced as much as possible, so that the cost is increased.
[0083]
In the fourth embodiment, as shown in FIG. 8, the thickness of the fixing roller 112 of the fixing device 110 is set to t = 0.30 mm. Further, as shown in FIG. 9, two reinforcing springs 116 and 118 were inserted into the core metal 115 of the fixing roller 112. The winding direction of the two reinforcing springs 116 and 118 is set to be toward the center of the fixing roller 112 in the longitudinal direction. The strength of the fixing roller 112 is maintained by these two reinforcing springs 116 and 118. The reinforcing springs 116 and 118 have a wire diameter of 1.0 mm or less that does not affect the heat capacity, and the reinforcing springs 116 and 118 are coated with heat-resistant black.
[0084]
As shown in FIG. 9, the reason why the two reinforcing springs 116 and 118 inserted inside the core bar 115 are installed so that the winding direction is directed to the center of the fixing roller 112 in the longitudinal direction is as follows. This is because the reinforcing springs 116 and 118 move in the winding direction due to the load of 54, and if the winding directions of the springs are in one direction, the springs are offset. Here, as described above, the two reinforcing springs 116 and 118 are installed such that the winding direction is directed to the longitudinal center of the fixing roller 112. As a result, the reinforcing springs 116 and 118 tend to move in the direction toward the center in the longitudinal direction of the fixing roller 112 due to the heat and the load of the pressure roller 54, so that the reinforcing springs 116 and 118 press against each other to balance the position. I can take it.
[0085]
In addition, heat-resistant black coating is performed on the reinforcing springs 116 and 118. The reason for this is to improve the thermal sensitivity of the reinforcing springs 116 and 118 themselves and to minimize the amount of movement caused by heat and the load of the pressure roller 54 by increasing the friction coefficient of the surfaces of the reinforcing springs 116 and 118. is there.
[0086]
The surface of the fixing roller 112 is coated with a fluorine-based PTFE / PFA mixed resin paint to improve the releasability. The pressure roller 54 has a configuration in which a heat-resistant release layer 54b having elasticity such as silicone rubber is formed on the outer peripheral surface of a metal core 54a. By pressing the outer peripheral surface of the release layer 54b against the fixing roller 112 from below, a fixing nip portion 114 is formed between the fixing roller 112 and the pressure roller 54. The width of the fixing nip portion 114 is set so that the toner on the recording medium can be suitably heated and pressed.
[0087]
The thermistor 60 is in contact with the outer peripheral surface (front surface) of the fixing roller 112, and measures the temperature of the outer peripheral surface of the fixing roller 112. The temperature measured by the thermistor 60 is transmitted to the control device 62 (CPU). Based on the temperature information transmitted to the control device 62, the phase and frequency of the AC voltage of an AC power supply (not shown) for supplying electricity to the halogen heater 56 are controlled by the triac 64. By controlling in this manner, the power supplied to the halogen heater 56 is controlled to control the temperature of the fixing roller 112. As a result, when the temperature detected by the thermistor 60 is lower than a predetermined set temperature, the energization is controlled so that the halogen heater 56 is heated. On the other hand, when the temperature detected by the thermistor 60 is higher than a predetermined set temperature, the energization is controlled so that the temperature of the halogen heater 56 decreases. With such control, the outer peripheral surface of the fixing roller 52 is adjusted to a constant temperature at the time of fixing.
[0088]
In the technique of the fourth embodiment, the heat capacity of the fixing roller 112 is reduced because the thickness of the fixing roller 112 is reduced. For this reason, as shown in FIG. 10, the rise time (the time from when the roller is completely cooled (at room temperature) to when the temperature rises to the fixing temperature T2) can be reduced to １ ／. Also, by using the fixing roller 112 having a small heat capacity on the toner fixing surface side, the heat capacity of the fixing nip portion 114 is also reduced. As a result, the time required for the fixing nip 114 to reach a temperature at which the toner has viscosity can be reduced, and the temperature of the fixing nip 114 during standby (during standby) falls within a range of 140 ° C. to 110 ° C. Can be controlled to be Therefore, it is easy to prevent the molecular weight distribution of the toner from shifting to the polymer side, and the fixing roller 112 is less likely to be stained with the toner. Therefore, the durability life of the fixing device 110 can be extended. In addition, since the start-up time is fast even when the apparatus stands by at a low temperature, it is not necessary to increase the power supplied to the halogen heater 56, and the cost can be reduced.
[0089]
According to the technique of the fourth embodiment, as shown in FIG. 11, when image formation (printing) is completed and each roller stops rotating and enters standby, the fixing roller 112 and the heat The temperature is controlled at a temperature Ts (100 ° C.) equal to or lower than the temperature (T1) at which the toner has the highest viscosity so that the toner attached to the pressure roller 54 is not polymerized and fixed. For this reason, the fixing nip portion 114 _S Is kept.
[0090]
In the fourth embodiment, since the fixing roller 112 having a small heat capacity is used, the standby temperature T _S The rise time is fast even if it is low. For this reason, when there is no rotation control before toner removal (control for keeping the fixing nip portion 114 at the temperature T1 for a predetermined time), the time until printing is completed is equivalent to that of the fixing roller having a thickness t = 0.85 mm. is there. Since the used toner is the same as the toner used in the first to third embodiments, the temperature T1 at which the toner has the highest viscosity is 140 ° C. In the fourth embodiment, the temperature control of the above-described second and third embodiments is also performed.
[0091]
Prior to the start of image formation (printing), the fixing nip is set to a temperature T1 (140 ° C.) at which the toner has the highest viscosity without rotating the fixing roller 112 (while the fixing roller 112 is stopped). Power is supplied to the halogen heater 56 so that the portion 114 is formed. The fixing nip 114 is provided at the standby temperature T _S To the idle rotation temperature T1 in about 2 seconds. Immediately after the fixing nip 114 reaches the temperature T1, the fixing roller 112 is started to rotate, and these rollers are rotated for 8 seconds in order to give the toner adhering to the fixing roller 112 and the pressure roller 54 a viscosity. Thereafter, the temperature of the fixing nip 114 is raised to the fixing temperature T2 (175 ° C.) in about 4 seconds. After the temperature of the fixing nip 114 reaches the fixing temperature T2 (175 ° C.), the recording medium reaches (enters) the fixing nip 114.
[0092]
The time required for the toner attached to the fixing roller 112 and the pressure roller 54 to have viscosity is 2 seconds longer than that shown in FIG. 3 because the heat capacity of the fixing nip portion 114 is reduced by using the fixing roller 112 having a small heat capacity. I was able to shorten it.
[0093]
While the recording medium passes through the fixing nip portion 114, the offset toner adhered to the fixing roller 112 and the pressure roller 54 has a viscosity. Therefore, the offset toner is transferred to the recording medium having poor releasability and fixed. It is removed from the roller 112 and the pressure roller 54. Since the offset toner transferred to the recording medium is not the fixed toner accumulated, it is invisible to the naked eye. Further, since the thickness of the fixing roller 112 is small and the heat capacity is small as compared with the case where the fixing roller having the thickness t = 0.85 mm is used (the case shown in FIG. 3), compared to the case of FIG. The time required to complete the paper discharge was reduced by 2 seconds.
[0094]
After the image formation is completed, the fixing roller 112 and the pressure roller 54 stop. When these are stopped, the toner adhering to the fixing nip 114 may be polymerized and fixed. Therefore, in order to prevent the toner from sticking, the fixing nip portion 114 is maintained at a temperature Ts (here, 100 ° C.) equal to or lower than the temperature (T1) at which the toner has the highest viscosity. Thereby, it is possible to reliably prevent the toner from being fixed in the fixing nip portion 114.
[0095]
Each time image formation (printing) is started, the toner adhering to the fixing roller 112 and the pressure roller 54 is given a viscosity while maintaining the fixing nip portion 114 at the temperature T1 (140 ° C.) where the toner has the highest viscosity. For this purpose, the rollers 112 and 54 are rotated for 8 seconds, and then the fixing nip 114 is heated to the fixing temperature T2 (175 ° C.). By controlling the temperature of the fixing nip 114 in this way, it is possible to remove toner stains over the entire outer peripheral surfaces of both the fixing roller 112 and the pressure roller 54. Thus, accumulation of dirt such as toner on the rollers 112 and 54 can be prevented.
[0096]
In the present embodiment, as in the second embodiment, when a test is performed in which the recording medium is stopped in the fixing nip unit 114 for 10 seconds and restarted every ten sets at 2 sheets / 10 minutes of intermittent durability, and then restarted. The same result as in the embodiment was obtained.
[0097]
By controlling the temperature of the fixing nip 114 as described above, the life of the fixing device 110 can be extended, and the traveling distance of the photosensitive drum and the transfer roller can be reduced to about １ ／. For this reason, the durable life of the fixing device 110 can be extended, and the time from the start of printing to the completion of discharge can be shortened, so that the energy consumption efficiency can be reduced by about 30%.
[0098]
【The invention's effect】
As described above, according to the fixing device of the present invention, even when the toner adheres to the pair of fixing rotators, the fixing nip portion is kept at the predetermined maximum while the pair of fixing rotators are stopped (during standby). Since the heating means is controlled so as to have a temperature equal to or lower than the viscosity temperature, the toner adhering to the pair of fixing rotators does not polymerize and does not adhere to the fixing rotator. Further, before the recording medium is conveyed (fixed) while nipping the recording medium in the fixing nip portion, the fixing nip portion is rotated at the maximum viscosity temperature and idles, so that the toner adhered to the pair of fixing rotators has a high viscosity. (High-viscosity toner). Thereafter, fixing is started at the fixing temperature, so that the high-viscosity toner is transferred (offset) to a recording medium having poor releasability. Therefore, the toner hardly accumulates on the pair of fixing rotators. Since the toner hardly accumulates on the pair of fixing rotators, the amount of the toner transferred to the recording medium is so small that it is invisible.
[0099]
Here, the pair of fixing rotators may rotate within the range of 10 seconds or more and 15 seconds or less when the pair of fixing rotators rotate idle before the recording medium is conveyed while nipping the recording medium in the fixing nip portion. In the case where the toner rotates idly for a time, the toner adhered to the pair of fixing rotators more surely has a high viscosity, so that the toner is more reliably transferred to the recording medium. As a result, the toner hardly accumulates on the pair of fixing rotators.
[0100]
Further, the predetermined maximum viscosity temperature is such that when a predetermined amount of toner is put into the fixing nip portion of the pair of fixing rotators and the pair of fixing rotators are rotated, the toner is rotated by the pair of fixing rotators. The highest stringing temperature between the bodies ensures that the toner exhibits the highest viscosity.
[0101]
Further, when the pair of fixing rotators are stopped while the recording medium is being conveyed while nipping the fixing nip portion, when the pair of fixing rotators are rotated again to start fixing, Prior to the start of fixing, the pair of fixing rotators are idled at the maximum viscosity temperature for a predetermined time, and immediately thereafter, the fixing nip is heated to the fixing temperature to remove the recording medium for cleaning. In the case where the recording medium is conveyed while being pinched by the fixing nip portion, the toner may adhere to the pair of fixing rotators by stopping the pair of fixing rotators while the recording medium is being conveyed while pinching the fixing nip portion. However, before the fixing is resumed, the idle rotation and the cleaning recording medium are conveyed, so that the toner attached to the pair of fixing rotators is transferred to the cleaning recording medium. That. Therefore, the toner hardly accumulates on the pair of fixing rotators.
[0102]
Still further, prior to transporting the recording medium while nipping the recording medium in the fixing nip portion, the operation in which the pair of fixing rotators idle without holding the recording medium in the fixing nip portion is performed based on a printing rate. If it is less than the predetermined printing rate, the idle rotation is not performed when the printing rate is less than the predetermined printing rate, and the idle rotation is performed when the printing rate exceeds the predetermined printing rate. Wear can be suppressed.
[0103]
Further, when fixing the toner having the maximum viscosity temperature in the range of 120 ° C. to 150 ° C. to the recording medium, the maximum viscosity temperature can be set in the range of 120 ° C. to 150 ° C.
[0104]
Furthermore, when one of the pair of fixing rotators has a reinforcing spring for reinforcing the one fixing rotator inserted therein, one of the pair of fixing rotators is provided. Since the thickness of the fixing nip can be reduced, the temperature of the fixing nip can be easily controlled.
[0105]
Further, according to the image forming apparatus of the present invention, it is possible to form a good image free from toner contamination on a recording medium.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating a laser beam printer as an example of an image forming apparatus in which an embodiment of a fixing device according to the present invention is incorporated.
FIG. 2 is a side view schematically showing a fixing device.
FIG. 3 is a graph showing control of a fixing roller surface temperature.
FIG. 4 is a schematic diagram illustrating an apparatus for measuring the viscosity of a toner.
FIG. 5 is a schematic diagram illustrating a fixing device according to a third embodiment.
FIG. 6 is a graph showing a predicted adhesion toner.
FIG. 7 is a graph showing a relationship between a printing rate and a change in reflection density caused by toner adhesion.
FIG. 8 is a schematic diagram illustrating a fixing device according to a fourth embodiment.
FIG. 9 is a cross-sectional view schematically illustrating a fixing roller.
FIG. 10 is a graph showing the relationship between the thickness of the fixing roller and the temperature of the fixing nip.
FIG. 11 is a graph showing the relationship between the surface temperature of a fixing roller and time.
[Explanation of symbols]
50,110 Fixing device
52,112 Fixing roller
54 Pressure roller
56 Halogen heater
58 Fixing nip
60 Thermistor
62 Control device

Claims (8)

In a fixing device for fixing a toner image on a recording medium by transporting a recording medium carrying an unfixed toner image while nipping the recording medium in a fixing nip portion formed by pressing a pair of fixing rotators against each other,
Heating means for heating the fixing nip portion,
Temperature control means for controlling the temperature of the heating means,
The temperature control means includes:
While the pair of fixing rotators are stopped, the fixing unit controls the heating unit so that the fixing nip portion has a temperature equal to or lower than a predetermined maximum viscosity temperature, and
Prior to transporting the recording medium while nipping the recording medium in the fixing nip portion, when the pair of fixing rotators rotate idle without clamping the recording medium in the fixing nip portion, the fixing nip portion has the maximum viscosity temperature. Controlling the heating means so that
When the recording medium is conveyed while being held between the fixing nip portion, the heating unit is controlled so that the fixing temperature is higher than the maximum viscosity temperature. The pair of fixing rotators,
Prior to transporting the recording medium while nipping the recording medium in the fixing nip portion, the pair of fixing rotators idle idle for a time within a range of 10 seconds or more and 15 seconds or less when idle. The fixing device according to claim 1. The predetermined maximum viscosity temperature is:
When a predetermined amount of toner is put in the fixing nip portion of the pair of fixing rotators and the pair of fixing rotators are rotated, at a temperature at which the toner pulls the yarn most between the pair of fixing rotators. The fixing device according to claim 1, wherein: When the pair of fixing rotators are stopped while the recording medium is being conveyed while nipping the recording medium in the fixing nip portion, when fixing is started by rotating the pair of fixing rotators again, this fixing is performed. Before we start,
The pair of fixing rotators are idled at the highest viscosity temperature for a predetermined time, and immediately thereafter, the fixing nip is heated to the fixing temperature, and the cleaning recording medium is sandwiched between the fixing nips. The fixing device according to claim 1, wherein the fixing device is conveyed. The operation in which the pair of fixing rotators idle without holding the recording medium in the fixing nip portion before the recording medium is conveyed while pinching the recording medium in the fixing nip portion is performed based on a printing rate. The fixing device according to claim 1, wherein: The fixing device according to claim 1, wherein the toner having the maximum viscosity temperature in a range of 120 ° C. or more and 150 ° C. or less is fixed on a recording medium. Either one of the pair of fixing rotators,
The fixing device according to any one of claims 1 to 6, wherein a reinforcing spring for reinforcing the one fixing rotary member is inserted therein. An image carrier on which a toner image is formed, a transfer device for transferring the toner image to a recording medium, and the fixing device according to any one of claims 1 to 7. Image forming apparatus.

Images